1. Field of the Invention
The present invention relates to a device for effecting height and longitudinal adjustment of a steering column of a motor vehicle and including a first adjusting device for height adjusting the steering column, a second adjusting device for longitudinal adjusting the steering column, a locking device having open and closed positions for simultaneously opening and closing the first and second adjusting devices and including a locking bolt, a bracket fixedly securable to a motor vehicle chassis, a guide member pivotally supported on the bracket, the locking bolt being supported in the guide member and extending through an opening formed in the bracket, the locking bolt being displaceable in the guide member in direction of a locking bolt axis and being displaceable, for the height adjustment of the steering column, together with the guide member, transverse to its axial extent and substantially transverse to an axial extent of steering shaft of the steering column, and a steering volume tube having a longitudinal bore extending in an axial direction of the steering shaft and through which the locking bolt extends, the steering volume tube being displaceable in the axial direction of the steering shaft to provide for longitudinal adjustment of the steering column.
2. Description of the Prior Art
A device of the above-described type for effecting longitudinal and height or angular adjustment of a steering column is disclosed in German Publication DE 196 43 203 A1. The adjustment devices in the known device are formed by first and second toothings which cooperate with a common locking device. The locking bolt of the locking device provides for two separable forcelocking circuits, namely, for effecting the height or angular adjustment and for effecting the longitudinal adjustment. The purpose of separation of the two adjustments is to be able to provide a break-off location in the forcelocking means (for the longitudinal adjustment) so that in case of a crash accident, only the circuit, in which the break-off location is provided, opens, with the other circuit remaining closed. As a result, during the crash accident, the steering column is displaced only axially, with the height or inclination of the steering column remaining unchanged.
The known device provides for a reliable fixation of the steering column in the closed position of the locking device and a relatively easy adjustment of the steering column in the open position of the locking device. However, with this device, closing of the locking device is not possible when even if only two teeth for the toothings for the longitudinal or height adjustment lie one above the other. Therefore, before closing of the locking device, the position of the longitudinal and height adjustment of the steering column, the braking friction, need be overcome. This position should be easily changeable, and the changing should be conducted until the locking device can be closed. To prevent superimposition of the teeth, a device, which would prevent the superimposition of two teeth during closing of the locking device, has been suggested. However, the proposed device is unreliable and its use is connected with increased costs of its production. The superimposition of teeth takes place in particular in the adjusting device for the height adjustment as the forces generated by this device are larger than the forces generated by the length adjusting device. Therefore, the teeth of the height-adjustment toothing need be formed stronger and higher.
Prior art also discloses the use of lamella stacks for securing and adjusting of steering columns. Adjusting devices with lamella stacks are disclosed in European Publications EP 0802104A1, EP 671308A1, German Publication De-OS 2412,696 and DE-OS1780061, and a British Publication GB2092966A. In the disclosed publications a single lamella stack is used for securing both the longitudinal and height adjusting positions. Because of large holding forces required for height adjustment, the lamella stack should include a large number of lamellas or they should have large cooperating surfaces. This results in a substantial friction even in the open position of the locking device which requires an application of a large force by a user in order to overcome the friction during the height adjustment.
Accordingly, an object of the present invention is to provide a device with which adjusting device for the height adjustment can be easily closed, with the height adjustment being easily effected, and without much wear.
This and other objects of the present invention, which will become apparent hereinafter, are achieved by providing a device in which the first adjusting device comprises a lamella stack formed of alternating large and small lamellas through which the locking bolt extends, first and second clamping plates arranged on opposite side of the lamella stack for clamping same in a closed position of the first adjusting device, and spring means for distancing the first and second clamping plates further away from each other in an open position of the first adjusting device, with the large lamellas being arranged in or on the bracket with a possibility of changing of spacing therebetween but without a possibility of displacement in a direction of the height adjustment of the steering column, with the large lamellas having each an inner recess for enabling displacement of the locking bolt relative to the bracket in the open position of the first adjusting device to enable the height adjustment of the steering column, and with the small lamellas being arranged for displacement in an axial direction of the locking bolt but without a possibility of displacement relative to the locking bolt in the direction of the height adjustment of the steering column, the small lamellas being displaceable with respect to the large lamellas in the open position of the first adjusting device upon the displacement of the locking bolt relative to the bracket.
By using a friction connection with a lamella stack, a sufficiently high holding force for the height-adjusting device is obtained also during a crash accident. During the tests, a crash-holding force should amount to more than 1000 kg. To this end, the lamella stack should include a corresponding number of lamellas or a smaller number of large surface lamellas. A stack formed of at least twelve large lamellas and at least eleven small lamellas, which are located between the large lamellas permits to achieve a desired holding force. The use of springs, which keep the clamping plates away from each other in the open position of the first adjusting device provides for floating retaining of the lamellas in a space between the clamping plates in the open position of the first adjusting device. The friction during the height adjustment remains, therefore, relatively small in relation to the obtainable holding force and despite large numbers of lamellas or large friction surfaces of the lamellas.
Advantageously, the second adjusting device is likewise based on the principle of friction connection and also preferably includes a lamella stack. For longitudinal adjustment much smaller holding forces are required, in the region of 400 kg. Correspondingly, the lamella stack can consist of fewer lamellas, which substantially reduces friction during the longitudinal adjustment. In principle, it is possible to use in a length-adjusting device only two friction plates which become preloaded against each other in the closed conditions of the locking device. With two friction plates, one of both cooperating surfaces can be formed with ribs for increasing friction in the closed condition of the locking device (which also permit to obtain more or less stronger form locking connection). One or both plates can also be provided with toothing.
The novel features of the present invention, which are considered as characteristic for the invention, are set forth in the appended claims. The invention itself, however, both as to its construction and its mode of operation, together with additional advantages and objects thereof, will be best understood from the following detailed description of preferred embodiments, when read with reference to the accompanying drawings.